Question

在我编写的程序中，当Textbox中有一个空字符串时，它将作为空字符串而不是NULL保存到数据库。

    Using DB As New wotcDB
        Dim u = (From t In DB.interview_ltu Where t.CONTROL = CONTROL And t.CLIENTCODE = CLIENTCODE).FirstOrDefault
        If u Is Nothing Then
            Dim i As New interview_ltu
            i.CONTROL = CONTROL
            i.CLIENTCODE = CLIENTCODE
            i.LTUnemp2Years = cboLTUnemp2Years.DBValue
            i.LTUnempExhast26wks = cboLTUnempExhast26wks.DBValue
            i.LTUComments = txtLTUnemployedCMT.Text
            i.LTUnempStart = txtLTUnempStart.DateValue
            i.LTUnempStop = txtLTUnempStop.DateValue
            DB.interview_ltu.Add(i)
            DB.SaveChanges()
        Else
            u.LTUnemp2Years = cboLTUnemp2Years.DBValue
            u.LTUnempExhast26wks = cboLTUnempExhast26wks.DBValue
            u.LTUComments = txtLTUnemployedCMT.Text
            u.LTUnempStart = txtLTUnempStart.DateValue
            u.LTUnempStop = txtLTUnempStop.DateValue
            DB.SaveChanges()
        End If
    End Using

我一直在做这个复杂的步骤，其中，我检查String.IsNullorEmpty每一个，但我觉得这不应该是必要的尤其是考虑到与此相关的在谷歌的问题暗示恰恰相反，人们正在尝试获取空字符串而不是NULL。

那么如何让Text框保存为NULL而不是空字符串？

编辑：

我已将此代码添加到我的上下文中;

Private Const StringType As String = "String"
Private Const SavingState As EntityState = EntityState.Added Or EntityState.Modified
Public Overrides Function SaveChanges() As Integer
    'when using on ObjectContext replace 'objectContext' with 'this',
    'and override SaveChanges(SaveOptions options) instead:

    Dim objectContext = CType(Me, IObjectContextAdapter).ObjectContext
    Dim savingEntries = objectContext.ObjectStateManager.GetObjectStateEntries(SavingState)

    For Each entry As Object In savingEntries
        Dim curValues = entry.CurrentValues
        Dim fieldMetadata = curValues.DataRecordInfo.FieldMetadata
        Dim stringFields = fieldMetadata.Where(Function(f) f.FieldType.TypeUsage.EdmType.Name = StringType)
        For Each stringField As Object In stringFields
            Dim ordinal = stringField.Ordinal
            Dim curValue = TryCast(curValues(ordinal), String)
            If Not curValue Is Nothing AndAlso String.IsNullOrWhiteSpace(curValue) Then ' AndAlso curValue.All(Char.IsWhiteSpace) Then
                curValues.SetValue(ordinal, Nothing)
            End If
        Next
    Next
    Return MyBase.SaveChanges()
    'SaveChanges(options) on ObjectContext
End Function

当它达到“For Each entry As Object in savingEntries”时，它只会跳到最后，因为它不会选择任何条目。我试图改变输入。没有成功。

Answer 1

查看以下链接。这可能会有所帮助

Link1

Link2

实体框架，文本框以“”而不是Nothing（NULL）的形式保存到数据库

1 个答案: